KR20240001109A - Plasma processing devices and heating devices - Google Patents

Abstract

In a plasma processing device using circularly polarized waves, in order to reduce the influence of reflected waves and enable efficient use of circularly polarized waves for plasma processing, a microwave source that generates microwaves and plasma generated by the microwaves are used. A plasma processing device having a plasma processing chamber installed inside to process an object to be treated, a waveguide section including a rectangular waveguide connected to a microwave source and a circular waveguide connected to the plasma processing chamber, wherein the inside of the circular waveguide is transmitted by microwaves. With plasma generated inside the plasma processing chamber, a reflected wave generator was installed to generate a reflected wave that cancels out the reflected wave propagating inside the circular waveguide from the side of the plasma processing chamber.

Description

Plasma processing devices and heating devices

The present invention relates to a plasma processing device and a heating device.

Plasma processing devices are used in the production of semiconductor integrated circuit devices. In order to improve device performance and reduce costs, progress has been made in device miniaturization. Conventionally, due to the two-dimensional miniaturization of devices, the number of devices that can be manufactured from a single substrate to be processed increases, lowering the manufacturing cost per device, and improving performance through miniaturization effects such as shortening the wiring length. come. However, when the dimensions of semiconductor devices reach the nanometer order, which is close to the size of an atom, the difficulty of two-dimensional miniaturization increases significantly, and efforts are being made to respond, such as by applying new materials or three-dimensional device structures. Due to these structural changes, the difficulty of manufacturing increases, the manufacturing process increases, and the increase in manufacturing cost becomes a serious problem.

If a minute foreign matter or contaminant adheres to a semiconductor integrated circuit element during manufacturing, it can cause a fatal defect. Therefore, semiconductor integrated circuit elements are manufactured in a clean room where foreign matter or contaminant is excluded and temperature and humidity are optimally controlled. . With the miniaturization of devices, the cleanliness of the clean room required for manufacturing increases, and enormous costs are required for the construction and maintenance of the clean room. Therefore, it is required to produce products using clean room space efficiently. From this perspective, semiconductor manufacturing equipment is strictly required to be miniaturized and cost-effective.

Additionally, the in-plane uniformity of the plasma treatment of the substrate being processed is also important. In the manufacture of semiconductor integrated circuit elements, a disk-shaped silicon wafer with a diameter of 300 mm is often used as a substrate to be processed. Many semiconductor integrated circuit elements are often manufactured on this silicon wafer, but if the in-plane uniformity of the plasma treatment is poor, there are cases where there are fewer good products that meet the specifications that can be obtained from a single silicon wafer. Likewise, the stability of plasma processing for each substrate to be processed is also important. If the quality of the plasma treatment is not stable and, for example, changes over time, the ratio of good products may similarly decrease.

In plasma processing devices that generate plasma by electromagnetic waves, devices that use microwaves with a frequency of about several GHz, typically 2.45 GHz, as the electromagnetic waves are widely used. In particular, there is a device that uses the Electron Cyclotron Resonance (hereinafter referred to as ECR) phenomenon, which occurs by combining microwaves and static fields. This device produces plasma relatively stably even under conditions where plasma production is normally difficult, such as extremely low pressure. It has excellent features such as being able to control the distribution of plasma by the distribution of the static field that can be generated.

In plasma processing devices using microwaves, magnetrons are widely used as microwave oscillators, but in recent years, oscillators using solid elements have also come to be used. Oscillators using solid elements have the advantage that the oscillation frequency and output are more stable than magnetrons, and various modulations can be easily applied. Additionally, rectangular waveguides, circular waveguides, coaxial lines, etc. are used to transmit microwave power. In addition, an isolator to protect the microwave oscillator and an automatic matcher to prevent impedance mismatch with the load are often used in combination.

As a prior art in this technical field, Patent Document 1 (Japanese Patent Application Laid-Open No. 9-270386) discloses a method for generating plasma with good uniformity by radiating microwaves to a plasma processing chamber from a slot antenna installed at the bottom of a cavity resonator. It is listed.

Additionally, Patent Document 2 (Japanese Patent No. 3855468) describes improving uniformity in the azimuthal direction by circularly polarizing microwaves using a circularly polarized wave generating means to generate plasma.

Japanese Patent Laid-Open Publication No. 09-270386 Japanese Patent No. 3855468 Publication

Patent Document 1 relates to generating plasma with good uniformity by radiating microwaves to a plasma processing chamber from a slot antenna installed at the bottom of a cavity resonator. Microwaves are supplied to the cavity resonator by TEM mode, which is the lowest-order mode of a coaxial line. However, in order to reduce reflection at the connection with the cavity resonator, a case is described in which the line length is connected via another coaxial line with an inner conductor diameter or outer conductor diameter of 1/4 wavelength.

In the configuration disclosed in this patent document 1, the TEM mode of a coaxial line in which the electromagnetic field does not change in the azimuth direction is used. Therefore, there is no need to temporally equalize in the azimuth direction using circularly polarized waves, and this event is not included.

In addition, the line length of the line for reducing reflected waves is limited to 1/4 wavelength, and the reduction of reflected waves using reflected waves at the top and bottom of the line is disclosed. In addition, there is a description of interposing a matching chamber in the connection part that causes reflection, and it is described that the height and diameter of the matching chamber are optimized to cancel out the reflected waves. However, the method for adjusting the height and diameter is limited to optimization technology, and there is no disclosure of the optimization method.

In addition, although Patent Document 1 discloses a method using a 1/4 wavelength line, there is no disclosure of a method for obtaining the optimal size for reducing reflected waves, and it is necessary to obtain the optimal size by repeating experiments by trial and error, resulting in a large number of problems. There are tasks that require effort, time, and money.

Additionally, in the case of a plasma processing device using circularly polarized waves, the structure for reducing the reflected waves needs to be a structure that does not inhibit circularly polarized waves. That is, when circularly polarized waves are incident on a structure for reducing reflected waves, it is necessary to ensure that the axis ratio of the transmitted electromagnetic waves does not deteriorate.

Additionally, when using a monitor device that optically observes a substrate to be processed through a waveguide for supplying the microwaves, it is necessary to avoid blocking the optically observed path by using the structure for reducing reflected waves.

Additionally, in Patent Document 2, it is described that uniformity in the azimuth direction is improved by circularly polarizing microwaves using a circularly polarized wave generating means to generate plasma, but in response to processing a disk-shaped substrate to be processed, Plasma processing devices are often configured to be axially symmetrical.

In the configuration disclosed in Patent Document 2, a circular waveguide is arranged coaxially with the central axis of the device, and microwave power is transmitted in TE ₁₁ mode, which is the lowest order mode of the circular waveguide. By making the device configuration coaxially symmetrical with the substrate being processed, we aim to generate uniform plasma in the azimuth direction. However, since the TE ₁₁ mode, which is the lowest order mode of a circular waveguide, is a mode that changes in the azimuth direction, plasma with good axial symmetry is generated by circularly polarizing the power distribution to be axially symmetric as the average of one microwave cycle.

As disclosed in Patent Document 2, when microwaves circularly polarized by a circularly polarized wave generating means are transmitted through a circular waveguide and a uniform plasma is generated in the azimuthal direction by the microwaves, the load side is viewed from the circular waveguide. If the reflection coefficient is large, there may be problems with various defects, such as poor operation of the circularly polarized wave generation means in response to circular polarization, poor ignition of plasma, and abnormal discharge due to large standing waves generated by large reflected waves. .

In addition, circularly polarized wave generation means are often designed based on the case where the reflection coefficient on the load side is zero. Therefore, if the reflection coefficient of the load is large, circularly polarized waves cannot be easily generated, making it impossible to realize a uniform electromagnetic field in the azimuth direction. There may be cases where it does not exist.

The present invention solves the problems of the prior art described above and, in a plasma processing device using circularly polarized waves, reduces the influence of reflected waves and makes it possible to efficiently use circularly polarized waves for plasma processing and heating. The device is provided.

In order to solve the above problems, the present invention includes a treatment chamber in which samples are treated with plasma, a high-frequency power source that supplies high-frequency power of microwaves through a circular waveguide, and a monitor device that optically monitors the plasma state through the circular waveguide; A plasma processing device comprising a circularly polarized wave generator disposed inside a circular waveguide and generating a circularly polarized wave, and a sample stand on which a sample is placed, comprising: a reflected wave generator disposed between the circularly polarized wave generator and the processing chamber and inside the circular waveguide; Additionally, the reflected wave generator generates a reflected wave that cancels out the reflected wave propagating from the processing chamber without interfering with the circularly polarized wave, and an optical path for optically monitoring the state of the plasma is formed in the reflected wave generator.

In addition, in order to solve the above-described problem, in the present invention, a heating chamber in which the sample is heated, a high-frequency power source that supplies high-frequency power of microwaves through a circular waveguide, and a circularly polarized wave disposed inside the circular waveguide and generating a circular polarized wave. A heating device including a generator, further comprising a reflected wave generator disposed between the circular polarized wave generator and the heating chamber and inside the circular waveguide, wherein the reflected wave generator cancels the reflected wave propagating from the heating chamber without interfering with the circular polarized wave. It is configured to generate reflected waves.

According to the present invention, by using a configuration that suppresses reflected waves, microwave power is efficiently supplied to the processing chamber, thereby expanding the range of conditions under which plasma can be generated and making it possible to utilize the microwave power more efficiently.

Additionally, in a plasma processing apparatus using a monitor device that observes a substrate to be processed optically or circularly polarized waves, it has become possible to secure an optical path without interfering with the circularly polarized wave.

1 is a cross-sectional view of the side of a microwave plasma etching device in the prior art.
Figure 2 is a cross-sectional side view of a microwave plasma etching device according to a first embodiment of the present invention.
3A (a) is a plan view showing a reflected wave generator according to the first embodiment of the present invention, and (b) is a side cross-sectional view.
Figure 3b (a) is a plan view showing a reflected wave generator with notches formed at two locations according to the first embodiment of the present invention, and (b) is a side cross-sectional view.
Figure 3c (a) is a plan view showing a reflected wave generator with notches formed at four locations according to the first embodiment of the present invention, and (b) is a side cross-sectional view.
Figure 4 is a cross-sectional side view of a heating device using microwaves according to a second embodiment of the present invention.
Figure 5 is a side cross-sectional view showing a reflected wave generator according to the first and second embodiments of the present invention.

The present invention is a plasma processing device that generates plasma by microwaves, and makes it possible to stably generate and maintain a spatially uniform plasma by efficiently and spatially uniformly supplying the power of the microwaves to the processing chamber. It relates to a plasma processing device that uses microwaves, and a heating device that makes it possible to efficiently and spatially uniformly supply microwave power to an object to be processed.

There is a scattering matrix as a known method of handling a microwave circuit that transmits electromagnetic waves such as microwaves. Considering a microwave circuit having ports for inputting and outputting a plurality (n) of microwaves, the incident wave and reflected wave at each port are defined. In addition to the physical microwave entrance and exit port, it also includes cases where multiple modes are considered for one entrance. For example, in a circular waveguide, multiple modes with different polarization planes can be set as ports on any surface of the circular waveguide.

The relationship between the incident wave vector whose element is the incident wave i _j (j = 1 to n) of each port and the reflected wave vector whose element is the reflected wave r _j (j = 1 to n), as shown in (Equation 1) The matrix representing is called the scattering matrix. When the number of input/output ports is one, the scattering matrix is a scalar and corresponds to the reflection coefficient. Each element of the scattering matrix is a complex number and has magnitude and phase or real and imaginary parts.

When the target microwave circuit is simple, the scattering matrix can be theoretically obtained in some cases, but even when the shape is complex, the scattering matrix can be obtained by performing electromagnetic field analysis using a numerical method such as the finite element method. Measurements can also be made using measuring instruments such as network analyzers.

[Formula 1]

n: Number of microwave input/output ports

For example, if the scattering matrix of a waveguide with an internal wavelength of λ and a length of L is small enough to ignore the loss,

[Formula 2]

It is known that it is displayed as . However, j is an imaginary unit.

Also, if the microwave circuit is reversible,

[Formula 3]

It is known that the scattering matrix becomes the target matrix. Additionally, it is known that when the microwave circuit is a passive circuit and is lossless, the scattering matrix becomes a unitary matrix.

Generally, a matcher is used to efficiently supply microwave power to a load. The matcher is installed in the transmission path between the microwave source and the load, and ideally functions to eliminate reflected waves generated from the load. In other words, using a matcher, reflected waves generated from the load are canceled out, and the power of the incident microwave is efficiently consumed by the load. The matcher has two ports, one on the microwave source side and the other on the load side, and can be modeled using a 2x2 scattering matrix. According to the reflection coefficient of the load, the internal parameters of the matcher are optimally controlled to eliminate reflected waves. As a matching device, a three-stub tuner in which three stubs of variable insertion length are installed in a rectangular waveguide, or an EH tuner in which branches of variable length are installed in the E-side and H-side of the rectangular waveguide are used. Additionally, an automatic matching machine is also used that automatically performs a matching operation by combining a mechanism that monitors the reflection coefficient of the reflected wave or the load, a drive mechanism and a control mechanism of the matching element in the matching machine, etc.

Additionally, there are cases where the quality of plasma processing can be improved by providing RF bias power to the substrate being processed. For example, in the case of plasma etching, a direct current bias voltage due to the mass difference between ions and electrons is generated in the substrate to be processed by RF bias with a frequency of about 400 kHz to 13.56 MHz, and this direct current bias voltage is used to separate the ions in the plasma. The quality of plasma processing can be improved by increasing the verticality of the processing shape or the processing speed.

Many structures have been proposed as a method of introducing microwaves into a plasma processing chamber. The microwave electromagnetic field distribution in the plasma treatment chamber and the resulting plasma distribution are affected by the microwave input method, and one of the factors that determines the uniformity of plasma treatment on the substrate to be processed is one of the factors.

A silicon wafer with a diameter of 300 mm is often used as a processing substrate used in the manufacture of semiconductor integrated circuits. Because of the need to perform uniform plasma processing on this disk-shaped substrate to be processed, the plasma processing apparatus is often structured to be axially symmetrical with respect to the center of the substrate to be processed. In addition, the supply of microwaves takes into account the axial symmetry of plasma processing, for example, by placing a coaxial line coaxially with the central axis and transmitting it in TEM mode, which is an electromagnetic field that does not change in the azimuth direction, or by transmitting a circular waveguide coaxially with the central axis. There are cases where the lowest order TE ₁₁ mode is circularly polarized and transmitted.

As an index for evaluating the degree of circular polarization, the magnitude of the maximum value to the minimum value of the magnitude of the microwave electric field vector within one cycle of the microwave is called the axial ratio, and this is sometimes used. With respect to the direction of movement of electromagnetic waves, if the electric field vector rotates clockwise, it is taken as negative, and if it rotates leftward, it is taken as positive. When the size of the axis ratio is 1, the size of the electric field vector does not change, and it becomes a completely circular polarized wave with a rotating direction. Also, if the size of the axis ratio becomes infinite, the polarization plane becomes linearly polarized without rotation. When a value other than this is taken, it is called elliptical polarization. In TE ₁₁ mode, which is the lowest order mode of the circular waveguide, the axis ratio is evaluated from the electric field vector on the central axis of the circular waveguide.

In general, circular polarization can be realized by superimposing linear polarization with different polarization planes and phase differences. Here, the polarization surface refers to the surface consisting of the wave propagation direction and the electric field vector. For example, by superimposing two waves of the same amplitude whose polarization planes are orthogonal and whose phase difference is 90 degrees, a completely circular polarized wave with an axial ratio of 1 can be realized. If the amplitude, phase difference, and polarization plane angle of two waves shift from these values, it becomes elliptical polarization. In general, when n linearly polarized waves of the same amplitude are overlapped, a completely circular polarization can be realized by the polarization planes forming an angle of 180 degrees/n and the phase difference being 180 degrees/n.

Generally, if there is a discontinuity in the microwave transmission path, reflected waves are generated. Even in the structure of injecting microwaves into a plasma processing chamber, for example, if a circular waveguide is enlarged into a step shape, reflected waves are generated due to this.

If the structure for realizing the optimal electromagnetic field distribution from the viewpoint of plasma uniformity within the plasma processing chamber becomes complicated, microwave power may not be transmitted efficiently within the processing chamber due to the influence of reflected waves generated from each part. Therefore, it is desirable to simplify the structure as much as possible, but compatibility with the desired electromagnetic field is often difficult. As a countermeasure, the matcher described above is used, but if the degree of mismatch with the load is too large, it may be difficult to secure a wide matching range corresponding to this, and a large standing wave is generated between the matcher and the load, which causes Abnormal discharge or power loss may become a problem.

Instant observation of plasma processing is effective for improving the quality of plasma processing and shortening processing time. There are various methods for instant observation depending on the plasma processing. For example, in the case of plasma etching processing, the substrate to be processed is directly observed during processing, the film thickness of the etching film is measured in real time, and processing is performed at the point when the desired film thickness is reached. There are cases where control is performed to stop . Compared to the case of no immediate observation, there are advantages such as stabilization of the processed film thickness and shortened processing time. Additionally, when an abnormality in the device is discovered through immediate observation, there is an advantage in that it is possible to take action such as immediately stopping processing.

Optical interference of the substrate to be processed can be used to measure the film thickness of the etched film. There is a method of irradiating reference light from the outside onto the substrate to be processed, a method of using a specific wavelength of plasma light emission, etc. In that case, it is necessary to prepare an observation window as a structure capable of optically observing the substrate to be processed during the plasma etching process.

A heating device that heats an object to be treated by irradiating it with microwaves is used. As objects to be treated, there are those corresponding to various materials such as food, wood, and ceramics. Compared to other types of heating devices, for example, heating devices that apply heat from a high-temperature heat source to the object to be processed through heat transfer, a device using microwaves can heat the object to be processed directly, resulting in lower power loss. In addition to being able to heat a small amount and efficiently, there is an advantage of being able to raise the temperature at high speed. Additionally, because microwaves have a short wavelength, it is possible to converge in a beam shape, and by focusing the microwaves only on the object to be treated, it is also possible to heat only a spatially desired area. Additionally, there is an advantage in that it is possible to selectively heat only a specific object to be treated by using the property that the loss of microwaves varies depending on the physical properties of the object to be treated.

On the other hand, in a heating device using microwaves, if the control of the electromagnetic field distribution of the microwaves is not appropriate, heating unevenness, such as a part of the object to be treated spatially not being heated, may occur due to the short wavelength. For example, when microwaves with a frequency of 2.45 GHz are used, in a closed space, standing waves tend to be generated at intervals of about 61 mm, which is half of the wavelength of 122 mm in free space, and heating unevenness may occur at this interval. As a countermeasure, there are cases where the object to be processed is moved or rotated, or a member that reflects microwaves is moved or rotated.

In a plasma processing device using microwaves, plasma is generated by supplying a strong electromagnetic field of microwaves into the processing chamber. Therefore, when the reflection coefficient of the load is large and the electromagnetic field within the processing chamber is relatively weak, it is clear that the ignition property of the plasma deteriorates. In addition, it is clear that when the reflection coefficient of the load is large, the standing wave generated by the overlap of the reflected wave and the incident wave becomes large, and the risk of abnormal discharge due to this also increases. In particular, when a matching device is used, it is clear that if the reflection coefficient exceeds the matching range of the matching device, the matching will be poor.

Additionally, even when the reflection coefficient of the load is within the matching range of the matching device, if the reflection coefficient of the load is large, the power dissipation power of the matching device decreases, and the risk of causing defects such as abnormal discharge increases. For example, in the case of a matching device using a stub, if the reflection coefficient of the load is high, the stub has no choice but to operate in a region where the insertion length within the waveguide is large, so the electric field generated between the tip of the stub and the waveguide wall increases, increasing the risk of abnormal discharge. .

In order to realize a reflected wave reduction structure that can secure an optical path without impeding circular polarization in a plasma processing device equipped with a monitor device for observing circular polarization or optically observing a substrate to be processed, the present invention , a plasma processing device that generates plasma using microwaves having a substantially axially symmetrical structure, transmitting microwave power for plasma generation through a circular waveguide operating in a single mode disposed on a central axis, and transmitting the microwave power for plasma generation within the circular waveguide. A circular polarized wave generator is provided for generating a circular polarized wave, and a discontinuity that does not interfere with the circular polarized wave is provided on a processing chamber side of the circular polarized wave generator. A reflected wave having a desired phase and amplitude is generated from the discontinuous part, and the generated reflected wave is provided. It was configured to cancel out the reflected waves generated from the plasma source structure on the treatment room side.

As a result, a structure with a generally arbitrary reflection coefficient is realized without interfering with the circularly polarized wave propagating within the circular waveguide, and the size and phase of the reflection coefficient can be adjusted to cancel out the reflected wave coming from the plasma processing chamber. I made it happen.

Additionally, in the case of a heating device using microwaves, there are problems similar to those of the plasma processing device described above. In other words, it is necessary to efficiently and uniformly supply microwave power to the member to be heated, and if the reflected wave in the transmission path of the microwave power is large, problems of power loss or abnormal discharge may occur. However, in the present invention, the waveguide This problem is solved by transmitting microwave power, providing a discontinuity that generates a desired reflected wave at a predetermined position in the waveguide, and configuring the reflected wave generated by this discontinuity to cancel out the reflected wave generated from the load side of the waveguide. did.

When the present invention is applied to a plasma processing device, by connecting the discontinuity of the structure as described below to the load, a structure that does not inhibit the circular polarized wave propagating within the circular waveguide and has a substantially arbitrary reflection coefficient was realized, and the size and phase of this reflection coefficient were adjusted to cancel out the reflected waves coming from the plasma processing room.

For example, the discontinuity is made up of a circular waveguide with a small inner diameter and a short length. For example, in the case of a circular waveguide with an inner diameter of 90 mm that transmits microwaves with a frequency of 2.45 GHz, a circular waveguide portion with an inner diameter of less than 90 mm and a length of 25 mm is installed as a discontinuous part. Qualitatively, if the inner diameter of the discontinuity is smaller, the reflection coefficient becomes larger, and the phase of the reflection coefficient can be adjusted by changing the position of the discontinuity. The wavelength inside the circular waveguide with an inner diameter of 90 mm is 202.5 mm at a frequency of 2.45 GHz. That is, by moving the position within the circular waveguide within the range of one wavelength, the phase can be adjusted to an arbitrary value between 0 and 2π radians. Additionally, since the discontinuity is composed of a circular waveguide, it does not inhibit circular polarization. As described above, circularly polarized waves can be described by superimposing linearly polarized waves with two orthogonal polarization planes, but since the discontinuity is composed of a circular waveguide, the scattering matrix of the discontinuity does not depend on the polarization plane of the incident wave. This is because the scattering matrix does not change no matter what angle the polarization plane is incident on.

FIG. 5 shows a model for numerically calculating the scattering matrix for the discontinuity formed by the circular waveguide 0502 with a small inner diameter and a short inner diameter described above. As described above, the circular waveguide 0502 forming the discontinuity is a circular waveguide 0502 with an inner diameter of less than 90 mm and a length of 25 mm, and circular waveguides 0501 and 0503 with an inner diameter of 90 mm and a length of 100 mm are connected before and after it. It is done. The central axis of circular waveguide 0502, which forms the narrow-diameter discontinuity, shares a central axis with circular waveguide 0501 and circular waveguide 0503. In addition, port 1_0504 and port 2_0505 are set in the circular waveguides (0501 and 0503), respectively.

Circular waveguides (0501 and 0503) with an inner diameter of 90 mm operating at a frequency of 2.45 GHz can propagate only the TE ₁₁ mode of the lowest sight mode, and the linear polarized wave of the TE ₁₁ mode is input or output to the two ports 0504 and 0505. do. The scattering matrix of this model is a 2×2 matrix.

Using the model shown in FIG. 5, in the case of a frequency of 2.45 GHz, the inner diameter of the circular waveguide 0502 forming the discontinuity is changed variously, and Helmholtz's equation, which is the basic equation of the electromagnetic system, is solved by the finite element method to obtain a scattering matrix was obtained numerically. The results are shown in Table 1.

In Table 1, the size (described in the amp column of the table) and phase (described in the arg column of the table) of each element (s ₁₁ , s ₁₂ , s ₂₁ , s ₂₂ ) of the scattering matrix are shown. As the diameter of the circular waveguide 0502 forming the discontinuity approaches 90 mm, the sizes of s ₁₁ and s ₂₂ tend to be small and the sizes of s ₁₂ and s ₂₁ tend to be large, and the size of the circular waveguide 0502 forming the discontinuity tends to be large. indicates that the reflection is small.

It can be seen that by selecting the diameter of the circular waveguide portion within the range shown in Table 1, the size or amplitude of the reflected wave generated in the circular waveguide 0502 forming the discontinuous portion can be adjusted to about 0.9. Additionally, the phase of the reflected wave can be adjusted by the distance between the load and the circular waveguide 0502 forming the discontinuity. That is, since the amplitude and phase of the reflected wave generated by the circular waveguide 0502 forming the discontinuity can be set generally arbitrarily, the reflected wave generated by the load can be canceled without interfering with the circular polarized wave.

Furthermore, since it is a reversible and lossless passive circuit as described above, s ₁₂ and s ₂₁ are equal, and the sum of the squares of the magnitude of s ₁₁ and the magnitude of s ₁₂ is 1. Additionally, since the structure is symmetrical for port 1 and port 2, s ₁₁ and s ₂₂ are equal.

[Table 1]

When the reflection coefficient of the load is known by methods such as measurement or calculation as described above, the reflected wave can be reduced by using the circular waveguide 0502 forming the discontinuity. Using the scattering matrix, the optimal discontinuity can be obtained.

When a circular waveguide 0502 forming a discontinuity of length L is connected to a load with a reflection coefficient R _p , the reflection coefficient R _p 'at the waveguide end surface of the circular waveguide 0502 forming a discontinuity is (Equation 2) ), using

[Formula 4]

It becomes. That is, by connecting the circular waveguide 0502 forming a discontinuity of length L, the phase of the reflection coefficient of the load can be controlled by the length L.

Additionally, the reflection coefficient R _p " when connecting the circular waveguide 0502 forming the discontinuity shown in FIG. 5 and Table 1 is

[Formula 5]

It becomes.

Also, from the conditions of reversibility, passive circuit, lossless, and symmetry, s ₁₁ =s ₂₂ and s ₂₁ =s ₁₂

[Formula 6]

In order to make R _p "zero

[Formula 7]

It has to be this way.

Since the phase of R _p 'can be arbitrarily controlled by the length L of the circular waveguide 0502 forming the discontinuity from (Equation 4), the size of the right side of (Equation 7) can be adjusted to match the size of R _p ' or R _p . All you have to do is do it. In other words, the size of R _p ' or R _p is a value between 0 and 1, so the size of the right side of (Equation 7) can be adjusted within the range of 0 to 1.

Table 1 shows the values of the right side of (Equation 7). It can be seen that the size can generally be adjusted within a range of about 0.9. That is, by selecting the length L of the circular waveguide 0502 that forms the optimal discontinuity, the entire reflected wave R _p " can ideally be adjusted to zero in the range where the reflection coefficient R _p of the load is less than about 0.9.

Embodiments of the present invention based on the above considerations will be described in detail with reference to the drawings. In all drawings for explaining the present embodiment, elements having the same function are given the same reference numerals, and repeated description thereof is omitted in principle.

However, the present invention should not be construed as being limited to the description of the embodiments shown below. It is easily understood by those skilled in the art that the specific configuration may be changed without departing from the spirit or spirit of the present invention.

Example 1

The present invention is an example in which the present invention is applied to a plasma processing device including a monitor device that optically monitors the plasma processing state using plasma generated by high-frequency power of microwaves and a circular polarization generator, and the optical path of the monitor device is secured. A plasma processing device is described, wherein a discontinuity that cancels out reflected waves without impeding circular polarized waves is disposed inside the circular waveguide and below the circular polarized wave generator.

As an example of a conventional plasma processing device on which the present embodiment is premised, a plasma processing device 100 that performs a conventional microwave plasma etching process will be described with reference to FIG. 1. Figure 1 shows a longitudinal cross-sectional view of the entire conventional plasma processing device 100. The plasma processing device 100 includes a microwave oscillator (0101), an isolator (0102), an automatic matcher (0103), a rectangular waveguide (0104), a measuring device (0105), a circular-rectangular converter (0106), and a circular waveguide (0107). ), a circular polarization generator (0108), a static field generator (0109), a cavity (0110), a dielectric window (0111), a shower plate (0112), a plasma processing chamber (0114), and a substrate to be processed (0113). It is equipped with a platform (0115) that can be used.

In this configuration, the microwave with a frequency of 2.45 GHz output from the microwave oscillator (0101) is transmitted through the isolator (0102) and the automatic matcher (0103) to the circular-rectangular converter (0106) by the rectangular waveguide (0104). . A rectangular waveguide (0104) was used operating in TE ₁₀ mode, the lowest order mode. The isolator (0102) functions to prevent reflected waves generated on the load side from entering and destroying the microwave oscillator (0101). The automatic matcher (0103) monitors the reflected wave or impedance on the load side and operates to automatically reduce the reflected wave by adjusting internal parameters. The automatic matcher 0103 may be a manual matcher in order to reduce device cost or simplify the device.

A magnetron was used as a microwave oscillator (0101). The circle-rectangular converter (0106) also serves as a corner that bends the direction of microwave travel by 90 degrees, and aims to miniaturize the entire device. A circular waveguide 0107 and a circular polarization generator 0108 in the circular waveguide are installed at the lower part of the circular-rectangular converter 0106, and convert microwaves incident as linearly polarized waves into circularly polarized waves. The circular waveguide 0107 is installed approximately on the central axis of the plasma processing chamber 0114, and circularly polarized microwaves generated by the circularly polarized wave generator 0108 are transmitted. On the load side of the circular waveguide (0107), a plasma processing chamber (0114) is provided with a cavity (0110), a dielectric window (0111), and a mounting table (0115) for placing the substrate to be processed (0113) through a shower plate (0112). It is installed. The central axis of the mounting table 0115 is set to coincide with the central axes of the plasma processing chamber 0114 and the circular waveguide 0107.

The cavity 0110 has the function of alleviating the central concentration of the injected microwave electromagnetic field. For the dielectric window (0111) and shower plate (0112), quartz was used because a material that has low loss to microwaves and is difficult to adversely affect plasma processing was required. A gas supply system, not shown, is connected to the plasma processing chamber 0114, and a small gap, not shown, between the dielectric window 0111 and the shower plate 0112 and a plurality of small supply holes provided in the shower plate 0112. The gas used for the etching process is supplied in the form of a shower. Additionally, a vacuum exhaust system (not shown) is connected to the plasma processing chamber 0114 through a pressure gauge (not shown) and a conductance variable valve for adjusting the exhaust speed (not shown).

With these devices, the plasma treatment chamber 0114 can be maintained at a desired pressure and gas atmosphere suitable for plasma etching treatment. There is a substrate to be processed (0113) in the plasma treatment chamber (0114), and plasma etching is performed using plasma generated by injected microwaves.

A silicon wafer with a diameter of 300 mm was used as the substrate to be processed (0113). An RF bias power supply (not shown) is connected to the processing target substrate 0113 via an automatic matcher, so that an RF bias voltage can be applied. The direct current bias voltage generated by this allows ions in the plasma to be drawn into the surface of the substrate to be processed, thereby improving the speed and quality of the plasma etching process.

A static field generator 0109 is installed around the plasma treatment chamber 0114, etc., so that a static field can be applied to the plasma treatment chamber 0114. The static field generator (0109) consists of an electromagnet using a plurality of solenoid coils and a yoke for efficiently applying a static field to the plasma processing chamber (0114) by reducing leakage magnetic flux. York was made of iron. By adjusting the current value flowing through the plurality of solenoid coils, the size and distribution of the static field applied to the plasma processing chamber 0114 can be adjusted. The static field is generally parallel to the central axis of the circular waveguide 0107 and parallel to the input direction of the microwave. A static field of 0.0875 Tesla that causes electron cyclotron resonance can be generated in the plasma processing chamber (0114), and its position can also be adjusted.

The circle-rectangular converter 0106 is equipped with a measuring device 0105 that optically observes the substrate to be processed 0113. The measuring device (0105) measures a substrate to be processed ( 0113) is being observed optically.

The optical axis of the measuring device 0105 is set at a position slightly offset from the center of the substrate 0113 to be processed. Therefore, the optical axis of the measuring device 0105 is located away from the central axis of the circular waveguide 0107.

By immediately observing the progress of the plasma etching process of the substrate to be processed, the speed and quality of the plasma treatment can be improved. For example, by stopping processing when the desired film thickness is reached, waste processing time can be reduced and processing precision can also be improved. For example, optical interference from the surface of the film to be treated and the underlying layer can be used to measure the film thickness. Interference light may be incident on the substrate to be processed from the outside, or light radiated from plasma within the processing chamber may be used.

FIG. 2 shows a plasma processing device 200 that performs plasma etching processing according to the first embodiment. The present invention is applied to the conventional example shown in FIG. 1, and common parts are assigned the same numbers and description is omitted. In the plasma processing device 200 according to the present embodiment, compared to the conventional plasma processing device 100 described using FIG. 1, the plasma processing device 200 is connected to the circular waveguide 0107 and installed on the load side of the circular polarized wave generator 0108. Reflected wave generators (0202(a) to (c)) were formed inside the waveguide (0201).

3A to 3C show the structure of the reflected wave generators 0202 (a) to (c) formed inside the waveguide 0201. 3A to 3C, (a) shows a top view and (b) shows an N-N cross-sectional view of (a).

The reflected wave generator 0202(a) in FIG. 3A has a structure consisting of a short circular waveguide with a narrowed inner diameter, similar to the discontinuous circular waveguide 0502 explained in FIG. 5, and the axial length of the narrowed diameter portion is 25 mm. The circular waveguide with a narrow diameter constituting the reflected wave generator 0202(a) shares a central axis with the circular waveguide 0201 connected above and below, and is not eccentric.

As explained in FIG. 1, the optical axis of the measuring device 0105 is set at a position slightly deviated from the center of the substrate to be processed 0113 placed on the stand 0115, so the optical axis of the measuring device 0105 is located in the circular waveguide 0107. ) is located away from the central axis. Therefore, the reflected wave generator 0202(a) interferes with the field of view of the measuring device 0105. To avoid this, it is necessary to install a notch on the side of the reflected wave generator 0202(a) in a portion where the reflected wave generator 0202(a) overlaps the field of view of the measuring device 0105.

The reflected wave generator 0202(b) shown in FIG. 3B has a structure in which four notches 0301 of the same shape are installed every 90 degrees in the azimuth direction on the reflected wave generator 0202(a) shown in FIG. 3A. Similarly, the reflected wave generator 0202(c) shown in FIG. 3C has a structure in which two notches 0302 of the same shape are provided at intervals of 90 degrees in the azimuth direction on the reflected wave generator 0202(a) shown in FIG. 3A.

As described above, it is necessary that the reflected wave generators 0202(a) to 0202(c) do not interfere with circular polarized waves. In the reflected wave generator 0202(a), it does not depend on the position of the polarization plane, and the scattering matrix becomes the same, so circular polarization is clearly not impaired.

In the reflected wave generators (0202(b), 0202(c)), for TE ₁₁ modes whose polarization planes are 90 degrees different in the azimuth direction, the notches (0301, 0302) are at the same position with respect to the polarization plane, so each TE ₁₁ The scattering matrices also become the same for each mode. Therefore, like the reflected wave generator (0202(a)), it does not interfere with circular polarized waves.

An example in which notches of the same shape are installed at four locations at equal intervals in the azimuth direction is shown in the reflected wave generator 0202(b) of FIG. 3B, but similarly, notches of the same shape may be installed at three locations at equal intervals. You can use 5 places at equal intervals or 6 places at equal intervals.

Providing the notches 0301 and 0302 has the effect of increasing the degree of freedom in setting the optical path of the measuring device 0105 that optically observes the substrate to be processed 0113 placed on the stand 0115.

By adjusting the size and phase of the reflected wave generated by the reflected wave generators 0202(a) to (c) shown in FIGS. 3A to 3C according to the reflection coefficient of the load, the reflected wave generators 0202(a) to (c) are Ideally, the reflection coefficient on the load side can be set to zero. The adjustment procedure is explained below. First, the scattering matrix of any one of the reflected wave generators 0202(a) to (c) is prepared by calculation or measurement as shown in Table 1. Additionally, the reflection coefficient of the load is obtained by measurement or calculation.

For example, the wavelength λ _g (m) within the tube of the TE ₁₁ mode, which is the lowest order mode of a circular waveguide of radius a (m), can be calculated using equation (3) for the frequency f (Hz).

[Formula 8]

However, c is the speed of light (m/s). For a circular waveguide with an inner diameter of 90 mm, the wavelength of TE ₁₁ mode is 202.5 mm from (Equation 8) for a frequency of 2.45 GHz.

Also, using (Equation 2), the scattering matrix of the TE ₁₁ mode circular waveguide of length L is obtained. Using the reflection coefficient of the load and (Equation 2) and (Equation 8), the reflection coefficient when a circular waveguide of length L is connected to the load can be obtained. If the loss of the circular waveguide can be ignored, the reflection coefficient after the circular waveguide is connected has the same size and only the phase changes compared to before the connection.

By changing the length L of the circular waveguide, the phase of the reflection coefficient of the load can be adjusted. Additionally, by connecting a reflected wave generator (equivalent to reflected wave generators 0202(a) to (c)), the entire scattering matrix can be obtained. In other words, if a circular waveguide of length L (corresponding to circular waveguides (0107 and 0201)) and a reflected wave generator (corresponding to reflected wave generators (0202 (a) to (c))) are connected to the load, it becomes a 1-port microwave circuit. , the overall reflection coefficient can be obtained from the scattering matrix, etc. The optimal values of the waveguide length L and the inner diameter of the reflected wave generator (corresponding to the reflected wave generators 0202(a) to (c)) can be obtained based on minimizing the reflected wave. By applying the obtained optimal value, the reflection coefficient on the load side can be reduced.

By preparing a large number of data corresponding to Table 1, the magnitude of the reflection coefficient on the load side can be made smaller.

As described above, in this embodiment, in the plasma processing device using plasma generated by high-frequency power of microwaves, a discontinuous portion (reflected wave generator) is loaded in the circular waveguide on the load side of the circular polarized wave generator, and the load According to the reflection coefficient, a wave that cancels out the reflected wave generated from the load is generated from the discontinuity, the amplitude and phase of the wave generated from this discontinuity are adjusted according to the reflection coefficient of the load, and the discontinuity has a narrow inner diameter. It is composed of a short circular waveguide, and the amplitude of the wave is adjusted by the shape (inner diameter of the throttle) and the phase is adjusted by the axial position of the throttle.

As a result, according to this embodiment, it is possible to realize a structure that does not inhibit circularly polarized waves propagating within a circular waveguide and has a substantially arbitrary reflection coefficient. Then, by adjusting the magnitude of the reflection coefficient and the phase of the circular polarization wave to cancel out the reflected wave coming from the plasma processing chamber side to the waveguide side, it became possible to suppress the loss of microwave power and suppress the occurrence of abnormal discharge.

By forming a plurality of notches (0301 or 0302) at symmetrical positions in the azimuthal direction with respect to the center in the reflected wave generator (0202(b) or 0202(c)) constituting the discontinuity, the symmetry of the positions of the notches (0301 or 0302) is achieved. In order not to interfere with circular polarization. To prevent microwave loss, a material with high conductivity was used, especially on the surface.

In this way, by providing the notch 0301 or 0302 on the reflected wave generator 0202(b) or 0202(c), the substrate to be processed 0113 placed on the stand 0115 in the plasma processing chamber 0114 can be connected to the measuring device ( 0105) to secure an optical path for optical observation. As a result, the plasma treatment can be observed in situ, making it possible to improve the quality of the plasma treatment.

That is, according to this embodiment, in the plasma processing device provided with an instantaneous observation means, it is possible to realize a structure that does not interfere with the circularly polarized wave propagating in the circular waveguide and has a substantially arbitrary reflection coefficient, and this reflection coefficient By adjusting the size and phase, it was possible to eliminate reflected waves coming from the plasma processing room. This solves the problem of power loss and abnormal discharge, makes it possible to efficiently and uniformly supply microwave power to the member to be heated, and improves the quality of the plasma treatment and shortens the processing time while performing immediate observation of the plasma treatment. It has become possible to realize it.

Example 2

As a second embodiment, a heating device having a microwave source, a circular waveguide, a circularly polarized wave generator installed within the circular waveguide, and a discontinuity provided on the output side of the circularly polarized wave generator, wherein the discontinuity is axially symmetric and does not impede the circular polarized wave. An example will be described in which a phosphor structure is used to generate a wave that cancels out reflected waves without breaking the axial symmetry of the microwave electromagnetic field and to heat the object to be treated with good uniformity.

Figure 4 shows a heating device 400 according to this embodiment. The heating device 400 according to this embodiment includes a microwave oscillator (microwave generator) 0401, an isolator 0402, a matcher 0403, a rectangular waveguide 0404, a measuring device 0405, and a circular-rectangular converter ( 0406), a circular waveguide (0407), a circularly polarized wave generator (0408), a reflected wave generator (0409), a heating chamber (0410), and a mounting table (0412) for placing the sample (0411).

In this configuration, the heating device 400 generates microwaves with a frequency of 2.45 GHz from the microwave generator 0401 and transmits them through the isolator 0402 and the matching device 0403 through the rectangular waveguide 0404. A rectangular waveguide (0404) with an inner cross-section of 109.2 mm × 54.6 mm operating in TE ₁₀ mode, the lowest order mode, was used. A magnetron was used as a microwave generator (0401). The isolator (0402) prevents reflected waves from the load from returning to the microwave generator (0401) and damaging them. The matcher (0403) functions to eliminate reflected waves caused by impedance mismatch of the load. A manual three-stub tuner was used as the matcher (0403), but an automatic matcher may also be used.

Microwaves are also introduced into the heating chamber 0410 by a circular waveguide 0407 through a circular-to-rectangular transducer 0406. The circular waveguide (0407) with an inner diameter of 90 mm operating in TE ₁₁ mode, the lowest order mode, was used. The circular-rectangular converter (0406) also has the effect of bending the direction of microwave propagation at a right angle.

There is a circular polarization generator (0408) within the circular waveguide (0407), which converts incident microwaves as linearly polarized waves into circularly polarized waves. Additionally, there is a reflected wave generator (0409) on the load side of the circular polarized wave generator (0408) and has the function of generating reflected waves. The reflected wave generator (0409) does not interfere with circular polarized waves. That is, when a circularly polarized wave is connected from the incident side, the reflected wave and the transmitted wave become circularly polarized waves. The reflected wave generator 0409 has the same structure as the reflected wave generators 0202 (a) to (c) that constitute the discontinuity formed inside the waveguide 0201 described using FIGS. 3A to 3C also in Example 1. , the same action and effect are obtained.

In the heating chamber 0410, there is a table 0412 on which the sample 0411 is placed and the sample 0411. The heating chamber 0410 has a generally cylindrical shape, and the mounting table 0412 is arranged substantially coaxially with the central axis of the cylindrical heating chamber 0410. Additionally, the circular waveguide 0407 is coaxially connected to the central axis of the heating chamber 0410. The circularly polarized wave generated by the circularly polarized wave generator 0408 is introduced into the heating chamber 0410 to heat the sample 0411.

In this configuration, since the polarization plane of the circularly polarized wave generated by the circularly polarized wave generator 0408 rotates at the frequency of the microwave, the absorbed power is smoothed during one cycle in the azimuthal direction with respect to the central axis of the circular waveguide 0407. In other words, uniform absorption power distribution in the azimuth direction can be realized by circular polarization. As a result, heating unevenness in the azimuth direction of the sample 0411 can be reduced.

In addition, as explained in Example 1, by adjusting the size and phase of the reflected wave by the reflected wave generator 0409 to the optimal value according to the reflection coefficient of the load, the reflected wave is reduced and the input power is effectively used to control the sample 0411. Can be used for heating. Additionally, the burden on the matching device (0403) can be reduced.

Additionally, as described above, the circular polarized wave generator 0408 is often optimized for matched loads, and in the case of mismatched loads, the axial ratio may deteriorate. However, by using the reflected wave generator 0409, the circular polarized wave generator ( 0408) malfunction can be prevented.

According to this embodiment, a discontinuous portion that generates a desired reflected wave is provided at a predetermined position in the waveguide, and the reflected wave generated by this discontinuous portion is configured to cancel out the reflected wave generated from the load side of the waveguide, thereby forming a member to be heated. It has become possible to supply microwave power efficiently and uniformly.

As mentioned above, the invention made by the present inventor has been described in detail based on examples. However, the present invention is not limited to the above examples, and it goes without saying that various changes can be made without departing from the gist of the invention. For example, the above-described embodiments have been described in detail to easily explain the present invention, and are not necessarily limited to having all the described configurations. Additionally, for some of the configurations of each embodiment, it is possible to add, delete, or replace other configurations.

100, 200 plasma processing device
0101, 0401 microwave oscillator 0102, 0402 isolator
0103 automatic matcher 0104, 0404 rectangular waveguide
0105, 0405 Optical observation measuring instrument
0106, 0406 circular-rectangular converter 0107, 0201, 0407 circular waveguide
0108, 0408 Circular polarization generator 0109 Static field generator
0110 Joint Department 0111 Genome Window
0112 shower plate 0113 substrate to be processed
0114 Plasma processing room 0115, 0412 platform
0202, 0202(a), 0202(b), 0202(c), 0409 reflected wave generator
0301, 0302 notch 0403 matcher
0410 heating chamber 0411 sample
0501 circular waveguide
0502 Circular waveguide forming a discontinuity 0503 Circular waveguide
0504 Port 1 0505 Port 2

Claims (8)

A processing chamber in which the sample is treated with plasma, a high-frequency power source that supplies high-frequency power of microwaves through a circular waveguide, a monitor device that optically monitors the plasma state through the circular waveguide, and a circular polarized wave disposed inside the circular waveguide. In a plasma processing device including a circular polarized wave generator and a sample stage on which the sample is placed,
Further comprising a reflected wave generator disposed between the circular polarized wave generator and the processing chamber and inside the circular waveguide,
The reflected wave generator generates a reflected wave that cancels out the reflected wave propagating from the processing chamber without interfering with the circular polarized wave,
A plasma processing device, characterized in that an optical path for optically monitoring the state of the plasma is formed in the reflected wave generator. According to paragraph 1,
A plasma processing device, characterized in that the central axis of the reflected wave generator is the same as the central axis of the circular waveguide. According to paragraph 1,
A plasma processing device, characterized in that the inner diameter of the reflected wave generator is defined based on the reflection coefficient of the load. According to paragraph 1,
A plasma processing device, wherein the position of the reflected wave generator in the direction of the central axis of the reflected wave generator is defined based on the reflection coefficient of the load. According to paragraph 3,
A plasma processing device, wherein the position of the reflected wave generator in the direction of the central axis of the reflected wave generator is defined based on the reflection coefficient of the load. According to paragraph 1,
A plasma processing device characterized in that the reflected wave generator has a plurality of notches. According to clause 6,
A plasma processing device characterized in that the notch portion is formed to be at the same position with respect to the polarization plane of the circularly polarized wave. A heating device comprising a heating chamber in which a sample is heated, a high-frequency power source that supplies high-frequency power of microwaves through a circular waveguide, and a circularly polarized wave generator disposed inside the circular waveguide and generating a circularly polarized wave,
Further comprising a reflected wave generator disposed between the circular polarized wave generator and the heating chamber and inside the circular waveguide,
A heating device, wherein the reflected wave generator generates a reflected wave that cancels out the reflected wave propagating from the heating chamber without interfering with the circularly polarized wave.